Thanks to both Wol and Eddie for pointing me to the --replace option and for not simply telling me to RTFM. Part of my confusion was based on my last attempt (years back) to find out if three drive RAID 1 was even an option. Just as before I found stuff that laughed at the mere idea of a three drive mirror. Seems people were getting too tied up on the word "mirror", which is not really a proper name for it in my view. The mirror copy of myself when looking into a mirror is *not* the same in me in so many ways. Oh, and now I think I understand that hardware RAID rarely or never allows it but Linux md RAID has it now and maybe had it the whole time. That said, I really should have slogged thru the man page better. It does seem that --replace includes the key feature that I want: "the device remains in service during the recovery process to increase resilience against multiple failures." So, just in case somebody wants to see if they can find anything I missed, here is my current plan... 1. Partition new drive (plugged in via external SATA dock) #fdisk /dev/sdc (make it an exact match of sda/sdb unless it turns out to be smaller, in which case I can shrink /boot to make room.) 2. Replace sda partition with sdc partition for each RAID. (Could do all at once but feels safer to do one at a time.) #mdadm /dev/md123 --replace /dev/sda7 --with /dev/sdc7 #watch /proc/mdstat #mdadm /dev/md125 --replace /dev/sda6 --with /dev/sdc6 #watch /proc/mdstat #mdadm /dev/md126 --replace /dev/sda3 --with /dev/sdc3 #watch /proc/mdstat #mdadm /dev/md1 --replace /dev/sda5 --with /dev/sdc5 #watch /proc/mdstat #mdadm /dev/md4 --replace /dev/sda2 --with /dev/sdc2 #watch /proc/mdstat 3. All RAIDs should be "active" and in "[UU]" status, with no sda partitions. #cat /proc/mdstat (Consider if this should only be done later/never so that sda can be a form of backup in case of issues during the post replace reboot.) 4. Prevent the old partitions from ever being pulled into the RAIDs. #mdadm --zero-superblock /dev/sda7 #mdadm --zero-superblock /dev/sda6 #mdadm --zero-superblock /dev/sda3 #mdadm --zero-superblock /dev/sda5 #mdadm --zero-superblock /dev/sda2 5. Make a new /boot on sdc. (using rsync since the language is taken from my daily cron and this is a tad quicker if I end up running it more than once.) (fstab line needing update: UUID=52b14d98-b284-41a0-a36f-459ae3ae12a7 /boot ext4 defaults 1 2) #mkfs.ext4 /dev/sdc1 #mkdir /bootnew #mount /dev/sdc1 /bootnew #rsync -a --delete /boot/ /bootnew #grub-install /dev/sdc #blkid /dev/sdc1 #vim /etc/fstab #umount /bootnew ; rmdir /bootnew 6. Power down and swap sdc into sda "slot". 7. Make sure that all RAIDs are "active" and in "[UU]" status: #cat /proc/mdstat -- Doug Herr -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
